1. Field of the Invention
The present invention relates to a heat exchanger and a water heater including the heat exchanger.
2. Description of the Related Art
The heat exchanger for use in a gas instantaneous water heater and other water heaters includes a water feeding pipe disposed in a casing; and a large number of heat absorbing fins disposed around the water feeding pipe in a region crossing an upper portion inside the casing of the water feeding pipe, of the piping route of the water feeding pipe. The heat exchanger performs heat exchange mainly using the heat absorbing fins.
Conventionally, a copper pipe has been used as the water feeding pipe. The copper pipe has advantages such as high thermal conductivity and excellent bending workability. On the contrary, the copper pipe has a known disadvantage that copper ions are dissolved under a specific water quality, causing pitting corrosion or so-called “blue water”. As a measure against the pitting corrosion and “blue water”, it is effective to perform a plating process on an inner surface of the copper pipe.
Japanese Patent Laid-Open No. 8-178585 discloses a technique of forming a tin plating layer on the inner surface of the copper pipe by causing an electroless tin plating solution to circulate inside the copper pipe after the heat exchanger is assembled. According to Japanese Patent Laid-Open No. 8-178585, the tin plating layer is described to block the copper ions from being dissolved and prevent the pitting corrosion or “blue water” from occurring.
However, conventionally the heat exchanger has a disadvantage that when the electroless tin plating solution is circulated through the copper pipe, the thickness of the tin plating layer becomes nonuniform, and thus cannot prevent the pitting corrosion or “blue water” from occurring.